Carboxyl containing polymers of vinyl or vinylidene monomers containing at least one terminal CH2═C< group are well known. Such polymers may be homopolymers of unsaturated polymerizable carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid and the like; or copolymers of said acid or anhydride monomers with (meth)acrylate esters, (meth)acrylamides, maleic anhydrides, vinyl esters, vinyl ethers, and styrenics; or copolymers with other vinyl or vinylidene monomers. Often, copolymers of these acids are cross-linked with small amounts of cross-linking agents. These materials are normally prepared by polymerization with a free radical catalyst in an organic medium in a closed vessel or autoclave equipped with stirring. During the course of such polymerizations, the polymer begins to precipitate from the solution as it is formed and flocculates and forms aggregates. The precipitated polymer is then recovered and dried to remove residual solvent. The polymer, which is now in a powder form, is used usually by dispersing it in water, neutralizing it, and adding it to a liquid to use its thickening ability. Such polymers are disclosed in U.S. Pat. Nos. 2,798,053; 3,915,921; 3,940,351; 4,062,817; 4,066,583; and 4,267,103.
Copolymers of a crosslinked polymer of polycarboxylic acids, such as polymers of acrylic acid, have become known commercially as “carbomers”. Carbomers are efficient rheology modifiers, and also find applications as polymeric emulsifiers and as suspension reagents in such items as lotions, personal care items due to their high thickening efficiency and their high yield stress.
Over the years, these polymers have been modified in various ways in attempts to improve their properties. For example, U.S. Pat. No. 4,996,274, incorporated herein by reference in its entirety, teaches improved properties of thickening and clarity by using specific polymerization media U.S. Pat. Nos. 5,288,814 and 5,468,797, both of which are incorporated herein by reference in their entireties, describe improved carbomers by using steric stabilizing polymeric surface active agents. These patents describe polycarboxylic acid polymers comprising interpolymers of olefinically unsaturated carboxylic acid or anhydride monomers containing at least one activated carbon to carbon olefinic double bond and at least one carboxyl group, and at least one steric stabilizing polymeric surface active agent (also called surfactant), having at least one hydrophilic moiety and at least one hydrophobic moiety and a linear block or random comb configuration, or mixtures thereof.
It is known that unsaturated carboxylic acid polymers can be modified by copolymerizing the carboxylic acid monomers with a comonomer, such as stearyl acrylate to impart hydrophobic properties to the resultant polymer.
There remains a need for improved carbomers having hydrophobes, especially non-hydrocarbyl hydrophobic monomers, directly incorporated into the polycarboxylic polymer backbone rather than incorporating hydrophobic properties indirectly through formation of interpolymers containing hydrophobic properties.